The invention relates to a method for checking the absence of voltage on a power electronics component connected to a high-voltage battery and an electric machine in a high-voltage network of a motor vehicle, which high-voltage network has a higher voltage than a low-voltage network of the motor vehicle, wherein the power electronics component has an intermediate capacitor, a passive discharge resistor, a plug-in terminal for at least one high-voltage load and a fuse connected upstream of the connector connection.
In the state of the art motor vehicles are known that have a low-voltage network, whose voltage is for example around 12V, and a high-voltage network, whose voltage is higher than that of the low-voltage network. The best-known examples for this are hybrid motor vehicles and electric motor vehicles. These have an electric machine, which can support propulsion of the motor vehicle and can also generate electrical energy from the movement of the motor vehicle. Further a high-voltage battery is usually assigned to the high-voltage network. High-voltage networks in the narrower sense include all networks of a motor vehicle whose voltage is greater than 60V DC voltage.
When such a high-voltage network is present, it is common to provide further high-voltage loads in the motor vehicle. Examples for such further loads are a charging device for the high-voltage battery (often also referred to as “On Board Charger” OBC), devices that are assigned to an air-conditioning system, for example a compressor, or high-voltage heating devices.
Since the electric machine generates an AC voltage and voltages may also have to be adjusted for other reasons, a power electronics component is provided in high-voltage networks of the described type, to which the electric machine and the high-voltage battery are usually securely fastened. Such a power electronics component also has for example a plug-in terminal via which further high-voltage loads can be connected by means of a connector and an appropriate cable connection. The power electronics component can have an inverter for converting AC voltage on the side of the electric machine into DC voltage on the side of the remaining high-voltage network and vice versa, and a rectifier. The power electronics component usually also has an intermediate circuit capacitor to which components for active discharge, and also a passive discharge resistor can be connected in parallel. A fuse, which is usually provided between the parallel connection of intermediate circuit capacitor and the discharge resistor and the plug-in terminal, separates the high-voltage load from the high-voltage source in case of a short circuit.
An important topic in motor vehicles with such a high-voltage network is the protection of persons from the high-voltage. In particular when maintenance work is performed on the motor vehicle, for example in a repair shop, it has to be possible to protect persons against the high-voltage in a simple yet reliable manner. While plug-in connections, for example that of the plug-in terminal, already have electric shock protection, it still has to be ensured that after deactivation of the high-voltage network no high-voltage remains in the system. This applies in particular to the power electronics component since there voltages may still remain for example on the intermediate circuit capacitor due to errors and/or the failure of discharge mechanisms. Thus procedures are known to ensure the absence of voltage also in the power electronics component.
Thus it is known in the state of the art to first separate the high-voltage battery from the high-voltage network. This is usually accomplished via contactors, which are provided in the high-voltage battery. In addition, a so-called “service disconnect” is usually provided, which removes the operating voltage for the contactors when being pulled and also interrupts the high-voltage pilot line. In order to secure the high-voltage network against re-activation this 12V service disconnect is usually secured with a lock.
In order to check the absence of voltage on the power electronics component it is known to open the power electronics component, for example by opening a lid of the power electronics component. Then it is checked with a measuring device at predetermined specific measuring sites in the power electronics component whether a high-voltage is still present. This has several drawbacks. On one hand opening the power electronics component and performing multiple voltage measurements in the power electronics component increases the required time until activation of the high-voltage network. The opening of the housing of the power electronics component also not only generates a high risk of contamination but may also compromise the tightness of the housing of the power electronics component. The procedure is also cost-intensive because a so-called touch guard insert is required in the power electronics component. Also for the activation itself the costs are high since the touch guard insert and the screws have to be replaced because the power electronics component has been opened.
There have also been efforts to determine the absence of voltage in the high-voltage network, specifically also in the power electronics component, by means of self-diagnosis in the motor vehicle, however, no accepted variant that satisfies the general safety requirements is yet known so that a manual disconnect and thus a manual testing of the voltage absence is still required and useful.
DE 10 2010 056 235 A1 relates to a method for checking a testing device for determining a voltage status of a high-voltage network of a motor vehicle. A test voltage for generating a predefined voltage state is introduced in a targeted manner, in particular by an external voltage source, and is measured with the testing device. The voltage state measured by the testing device is compared with the predetermined voltage state, wherein a deviation indicates the presence of an error.
DE 120 2010 012 154 A1 relates to a method for checking a state of an electric circuit of a motor vehicle. After querying a state it is checked whether the state is actually present. Concretely, the voltage of the electric circuit can be measured for the checking.
The subsequently published DE 10 2012 000 598 A1 discloses a motor vehicle high-voltage system with a fuel cell unit. A safety unit limits, at least in an inactive state of the drive device, the voltage in the high-voltage network and measures the voltage to enable monitoring the voltage.